To apply the aquatic insects occurring at the school swimming pools during off-season to environmental education, we gained their ecological information focussing on a few subjects : (i) species composition of the dragonfly larvae and other aquatic insects found in the swimming pools, (ii) life histories of the dominant dragonfly larvae, (iii) the reason why those species are dominant at a swimming pool, and (iv) species composition of phytoplankton, the food of chironomids which are prey of dragonfly larvae.Surveys and experiments for 2 years in Kyoto City and Tsu City revealed that (1) eight species of dragonfly larvae were found at the swimming pools of the primary schools in Kyoto City, especially Sympetrum striolatum imitoides was most common, on the other hand, the larvae of Orthetrum albistylum speciosum were dominant in Tsu City where S.striolatum imitoides is not distributed ; (2) the reason why larvae of S.striolatum imitoides are found so commonly at swimming pools is that, their life history pattern of laying eggs in October with adult eclosion the next June coincides with the non-use period of the pools, and females lay eggs directly into the water ; (3) Cosmarium was the most common phytoplankton at the swimming pools in Kyoto City.